Method of seperating fastener shanks from heads or frames

ABSTRACT

A device and method for removal of fasteners by Electro-discharge Machining (EDM) such that portions of the fastener, such as a flange, may be separated from other portions of the fastener, such as a shank.

RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 13/093,684, filed on Apr. 25, 2011, which claims priority toU.S. Provisional Patent Application 61/328,797, filed Apr. 28, 2010, andis a Continuation In Part of U.S. patent application Ser. No.12/603,507, the disclosures of which are incorporated by reference intheir entirety.

BACKGROUND

1. Field

This disclosure relates to electrical discharge machining (EDM).

SUMMARY

According to some exemplary implementations, disclosed is an EDM device,comprising: an erosion electrode configured to be advancedlongitudinally through a head of a fastener having a shank, the fastenerbeing fixed within a frame, wherein the erosion electrode has an outerradius less than an outer radius of the shank, the difference betweenthe outer radius of the erosion electrode and the outer radius of theshank defining an offset, wherein the erosion electrode is configured tocreate an eroded space within the fastener and maintain a ligamentwithin the shank, the ligament having a thickness defined by the offset.

The erosion electrode may be a hollow cylinder. The erosion electrodemay be a solid cylinder. The erosion electrode may be a plurality ofpins. The erosion electrode may be configured to be rotated as it isadvanced longitudinally. The erosion electrode may be configured to berotated about an axis of rotation corresponding to a central axis of thefastener.

The EDM device may further comprise: a power supply configured toprovide a voltage difference between the erosion electrode and at leastone of the fastener and the frame. The EDM device may further comprise:a ground electrode configured to contact at least one of the fastenerand the frame.

The offset may be configured to provide the ligament with the thicknessconfigured to sever under an external force that is within an acceptabletolerance of the frame. The offset may be configured to provide theligament with the thickness configured to sever under an intrinsic forcefrom the frame applied to the head of the fastener. The offset may bebetween about 0.010 inches and about 0.020 inches. The offset may bebetween about 0.020 inches and about 0.040 inches. The offset may bebetween about 0.040 inches and about 0.045 inches.

According to some exemplary implementations, disclosed is a method,comprising: providing an erosion electrode to a fastener in a frame, thefastener having a head extending beyond at least a portion of the frameand a shank at least partly within the frame; creating an eroded spacewithin the fastener, the eroded space having an outer radius less thanthe outer radius of the shank and extending through the head of thefastener, whereby a ligament of the shank is maintained, the thicknessof the ligament being defined by an offset between the outer radius ofthe eroded space and the outer radius of the shank.

Creating an eroded space may comprise: providing a voltage differencebetween the erosion electrode and the fastener. Creating an eroded spacemay comprise: advancing the erosion electrode longitudinally along theaxis of the fastener. Creating an eroded space may comprise: rotatingthe erosion electrode as it is advanced longitudinally.

The method may further comprise: applying an external force to at leastone of the shank and a flange of the head, whereby the ligament issevered and the flange is separated from the shank. The external forcerequired to sever the ligament may be within an acceptable tolerance ofthe frame. An intrinsic force from the frame may be applied to the headof the fastener. The ligament may be sufficiently thin to allow theintrinsic force from the frame to sever the ligament without requiringan external force. The frame may remain intact.

DRAWINGS

The above-mentioned features of the present disclosure will become moreapparent with reference to the following description taken inconjunction with the accompanying drawings wherein like referencenumerals denote like elements and in which:

FIG. 1 shows a sectional view of fastener in a frame;

FIG. 2 shows a sectional view of fastener in a frame;

FIG. 3 shows a bottom view of an erosion electrode and a bottom view ofa fastener;

FIG. 4 shows a sectional view of an erosion electrode approaching afastener;

FIG. 5 shows a sectional view of an erosion electrode penetrating afastener;

FIG. 6 shows a sectional view of an eroded space in a fastener;

FIG. 7 shows a sectional view of a head of a fastener removed from theshank of the fastener;

FIG. 8 shows a bottom view of an erosion electrode and a bottom view ofa fastener;

FIG. 9 shows a sectional view of an erosion electrode approaching afastener;

FIG. 10 shows a sectional view of an erosion electrode penetrating afastener;

FIG. 11 shows a bottom view of an erosion electrode and a bottom view ofa fastener;

FIG. 12 shows a sectional view of an erosion electrode approaching afastener;

FIG. 13 shows a sectional view of an erosion electrode penetrating afastener;

FIG. 14 shows a sectional view of an eroded space in a fastener;

FIG. 15 shows a sectional view of a head of a fastener removed from theshank of the fastener;

FIG. 16 shows a bottom view of an erosion electrode and a bottom view ofa fastener;

FIG. 17 shows a sectional view of an erosion electrode approaching afastener; and

FIG. 18 shows a sectional view of an erosion electrode penetrating afastener.

DETAILED DESCRIPTION

As used herein, “offset” is the difference between an outer radius of anerosion electrode and an outer radius of a shank, other workpiece, orportion thereof.

As used herein, “outer radius” of an erosion electrode corresponds tothe radially outermost limit or distance from a central axis of theerosion electrode, as determined at one or more points in time during aprocess.

As used herein, “eroded space” is a space that was previously occupiedby a workpiece and is created by an erosion process.

As used herein, “ligament” is a portion of a workpiece defined by aneroded space and a boundary of the workpiece (i.e., shank diameter).

As used herein, “external force” is any force selectably applied by auser to a fastener, other workpiece, or portion thereof. As used herein,“punch-out force” is a mechanical force provided to a fastener to causea portion thereof to dislodge in a direction of the punch-out force.

As used herein, “intrinsic force” is any force applied to fastener 10that exists while the fastener is in its originally installed state(i.e., prior to operations disclosed herein). An “intrinsic force” mayinclude one that exists and is applied to the fastener by virtue of aframe in which it is installed.

As used herein, “acceptable tolerance” of a frame is determined by atleast one of tensile strength (e.g., breaking strength) of a fastener,and tensile strength (e.g., yield strength) of the frame, based onapplicable safety guidelines, regulations, and desired outcomes.

According to some exemplary implementations, disclosed is an EDM devicefor facilitating separation of head 22 of fastener 10 from shank 30 offastener 10. As shown in the FIGS. 1 and 2, fastener 10 may includeshank 30 extending through at least a portion of frame 50. Shank 30 mayhave a known or determinable shape and geometry. For example, shank 30may be generally cylindrical having an outer diameter. As shown in FIGS.1 and 2, fastener 10 may include head 20 protruding from at least aportion of frame 50. Head 20 may include flange 22, corresponding to theportion of head 20 that extends radially beyond the outer diameter ofshank 30. As shown in FIG. 1, fastener 10 may include a fillettransition from head 22 to shank 30, wherein the diameter of fastener 10decreases in a somewhat gradual manner.

According to some exemplary implementations, devices, systems, andmethods of the present disclosure may be applicable to a variety offastener and frame configurations. Such configurations may includeprotruding or non-protruding, with or without sleeve about the fastener,threaded or non-threaded, with or without fitted collars, etc. Thosehaving ordinary skill in the art will recognize the variation andvariety of fasteners which may be modified or eroded with the disclosedmethods and devices, the modification or erosion thereof being withinthe scope of the present disclosure.

According to some exemplary implementations, as shown in FIG. 1, head 20may protrude from a surface of frame 50. According to some exemplaryimplementations, as shown in FIG. 2, head 20 may be flush with a surfaceof frame 50 (non-protruding). For example, frame 50 may include acountersink portion. While head 20 may extend only beyond some portionsof frame 50, it may simultaneously be substantially flush with thesurface of frame 50.

According to some exemplary implementations, fastener 10 may interfacewith at least a portion of frame 50. For example, fastener 10 may befitted within or threaded onto frame 50. Fastener 10 may interface witha collar (not shown) at a side of frame 50 opposite head 20 of fastener10. According to some exemplary implementations, it may be advantageousto facilitate removal of fastener 10 without separation thereof from acollar or other structure fixed thereto. For example, it may beadvantageous to remove fastener 10 or portions thereof in a directionopposite the side containing head 20.

According to some exemplary implementations, erosion electrode 100 of anEDM device may be of a variety of shape, sizes, and configurations.According to some exemplary implementations, erosion electrode 100 maybe configured to remove head 20, flange 22, or at least portions thereoffrom shank 30. For example, as shown in FIGS. 3, 4, and 5, erosionelectrode 100 may be a hollow cylinder. As shown in FIGS. 3 and 4,erosion electrode 100 may have outer radius 150 less than outer radius70 of shank 30 of fastener 10. Outer radius 150 of erosion electrode 100may correspond to the radially outermost limit or distance from acentral axis of erosion electrode 100, across one or more points duringa process. According to some exemplary implementations, as shown inFIGS. 3 and 4, the difference between outer radius 150 of erosionelectrode 100 and outer radius 70 of shank 30 may define offset 90.

According to some exemplary implementations, erosion electrode 100 maybe advanced to penetrate at least a portion of fastener 10. As shown inFIG. 6, erosion electrode 100 may be advanced longitudinally along anaxis. The axis may be coaxial with, parallel to, or otherwise alignedwith a central axis of fastener 10.

According to some exemplary implementations, erosion electrode 100 maybe configured to create eroded space 200 by an EDM process. For example,a voltage difference may be provided from a power supply between erosionelectrode 100 and at least one of fastener 10, frame base 50, and anycomponent in electric conductivity with one or more of the above. Adielectric fluid may be provided between erosion electrode 100 and atleast one of the above. At a given voltage, the dielectric fluid mayexperience breakdown, and a plasma event may occur, causing at least aportion of fastener 10 to become eroded, leaving eroded space 200 at thelocation of the plasma event. A series of plasma events may cumulativelydevelop eroded space 200.

As shown in FIGS. 4, 5, and 6, erosion electrode 100 may create erodedspace 200. Eroded space 200 may have a geometry corresponding to that oferosion electrode 100. For example, eroded space 200 may have an outerradius substantially equal to outer radius 150 of erosion electrode 100.Slight variation between outer radius of erosion electrode 100 and theouter radius of eroded space 200 is contemplated, inasmuch as an EDMprocess may erode a space that is either substantially similar to oridentical to the geometry of erosion electrode 100.

According to some exemplary implementations, creation of eroded space200 by erosion electrode 100 may define ligament 40. As shown in FIG. 6,ligament 40 may be a portion of fastener 10 that is defined by the outerradius of eroded space 200 (corresponding to outer radius 150 of erosionelectrode 100) and outer radius 70 of shank 30. The thickness ofligament 40 may be defined by offset 90. For example, the thickness ofligament 40 may be substantially equal to offset 90. By further example,the thickness of ligament 40 may be determinable based on offset 90.

According to some exemplary implementations, ligament 40 may facilitateseparation of flange 22 from at least a portion of shank 30. Forexample, as shown in FIG. 7, ligament 40 may be severed, such thatfastener 10 is divided into two disparate parts. The disparate parts mayinclude flange 22 and shank 30. Separation of flange 22 from shank 30may facilitate removal of shank 30 from frame 50 in a direction oppositethat of head 20 or flange 22.

According to some exemplary implementations, ligament 40 may be severedby an external force provided after creation of eroded space 200. Anexternal force may be applied to shank 30 in a direction opposite thatof head 20 or flange 22 (i.e., a “punch-out force”). The external forcemay be within an acceptable tolerance of frame 50. For example, frame 50may be configured to withstand a limited amount of force, based on itsstructure and composition. Acceptable tolerance of frame 50 may bedetermined by at least one of tensile strength (e.g., breaking strength)of fastener 10, and tensile strength (e.g., yield strength) of frame 50,based on applicable safety guidelines and regulations. For example, theexternal force may be determined to be any force under which ligament 40will rupture without causing plastic deformation of frame 50.

According to some exemplary implementations, ligament 40 may be severedby an intrinsic force from frame 50 applied to head 20 or flange 22 offastener 10. An intrinsic force may be any force applied to fastener 10that existed while fastener 10 was in its originally installed state(i.e., prior to operations disclosed herein). For example, frame 50 maybe under stress or pressure; head 10 or flange 22 of fastener 10 may beunder stress from a collar attached thereto at an end opposite head 20;or fastener 10 may hold frame 50 against another frame, where the twoframes may have a tendency to separate. Other intrinsic forces arecontemplated and ligament 40 may be responsive thereto.

According to some exemplary implementations, offset 90 may be configuredto yield ligament 40 with a thickness configured to sever under anexternal force or an intrinsic force. Based on materials, structure, andcomposition of at least fastener 10 and frame 50, features (e.g.,thickness) of ligament 40 required to yield a desired result may beknown or determinable (for example, by routine experimentation).

According to some exemplary implementations, fastener 10 has a filletradius, as shown in FIG. 1. According to some exemplary implementations,it is desirable to avoid erosion of frame 50 and to arrange for fastener10 to fracture at the bottom (most narrow portion) of the fillet radius.Such an arrangement may avoid leaving a burr on shank 30 once it isseparated from head 22. Such a burr in with diameter in excess of theremainder of shank 30 might damage frame 50 when shank 30 is driventhrough frame 50.

According to some exemplary implementations, larger offset 90 providesmore tolerance with regard to concentricity of erosion electrode 100 andshank 30. For example, a larger margin of error is allowed for aligningerosion electrode 100 with fastener 10 to avoid erosion of frame 50.According to some exemplary implementations, larger offset 90 requires alarger punch-out force to be applied to sever ligament 40.

According to some exemplary implementations, smaller offset 90 providesless tolerance with regard to concentricity of erosion electrode 100 andshank 30. For example, a smaller margin of error is allowed for aligningerosion electrode 100 with fastener 10 to avoid erosion of frame 50.According to some exemplary implementations, smaller offset 90 requiresa smaller punch-out force to be applied to sever ligament 40.

According to some exemplary implementations, offset 90 may be configuredto yield no ligament 40 (0 ligament size). For example, erosionelectrode 100 may have electrode radius 150 substantially equal to shankradius 70 of shank 50. Such a configuration may be used where erosioninto a “skin” of frame 50 (typically 0.05″-0.25″ thick) is acceptable,for example, where damage to the underlying portion of frame 50 isavoided. Such a configuration may be used where zero impact (punch-outforce) is tolerable. According to some exemplary implementations, wherea replacement fastener is provided to the same space, such replacementfastener may need to be oversize relative to the original fastener.

According to some exemplary implementations, offset 90 in the range ofabout 0.005 inches to about 0.010 inches is used in fragile or non-rigidstructures where the punch-out force must, should, or may be minimal. Inorder to minimize or avoid damage to frame 50 by erosion electrode 100,concentric alignment may be sufficiently accurate to provide a level ofconcentricity precision.

According to some exemplary implementations, frame 50 having a morefragile structure will require smaller offset 90 to reduce the forcerequired to sever ligament 40. For example, where frame 50 is acomposite airframe, offset 90 may be less than about 0.015625 inches. Inparticular, offset 90 may be between about 0.010 inches and about 0.020inches.

According to some exemplary implementations, offset 90 in the range ofabout 0.010 inches to about 0.015 inches is used in structures thattolerate moderate punch-out force. Accordingly, demands on concentricityare relaxed relative to more narrow offset 90.

According to some exemplary implementations, frame 50 having a somewhatless fragile structure may allow larger forces to act thereon, whereinoffset 90 may be larger. For example, where frame 50 is an aluminumairframe, offset 90 may be less than about 0.03125 inches. Inparticular, offset 90 may be between about 0.020 inches and about 0.040inches.

According to some exemplary implementations, offset 90 in the range ofabout 0.020 inches to about 0.025 inches is used where fastener 10 willbe subjected to tensile stresses so great that fastener 10 will fail(i.e., sever at ligament 40) when weakened by the process. For example,frame 50 having one or more portions may provide stress on fastener 10that cause it to readily separate into shank 30 and head 22 whensufficient erosion is provided. Such force and stress may be consideredintrinsic forces applied to fastener 10. An intrinsic force may be onethat exists and is applied to fastener 10 by virtue of frame 50.Intrinsic forces are contrasted with external forces, which requireintervention by a user. This characteristic reduces demands onconcentricity. Further, instantaneous “flash-burn” in composites may beminimized when fastener 10 fails. For fastener 10 of titanium or othersufficiently hard material, which is not under high forces, some degreesof punch-out force would be unacceptable where ligament 40 is notsufficiently thin.

Other, more durable structures for frame 50 may allow offset 90 to beless than about 0.0625 inches. In particular, offset 90 may exceed about0.040 inches.

According to some exemplary implementations, offset 90 may be nonzero,such that frame 50 is not affected (i.e., remains intact) by theoperation of erosion electrode 100.

According to some exemplary implementations, erosion electrode 100 maybe rotated about an axis while being advanced longitudinally.

According to some exemplary implementations, erosion electrode 100 mayinclude one or more point electrodes. As shown in FIGS. 8, 9, and 10, aplurality of point electrodes 100 a and 100 b may be provided androtated about an axis while advancing longitudinally. Erosion electrodes100 a and 100 b may cumulatively provide outer radius 150 defined by therotation about an axis. The rotation and advancement or point electrodes100 a and 100 b may result in an eroded space 200 similar to that causedby erosion electrode 100 as a hollow cylinder, as shown in FIG. 6.Accordingly, flange 22 may be removed in a manner as shown in FIG. 7.

According to some exemplary implementations, erosion electrode 100 maybe a solid cylinder, as shown in FIGS. 11, 12, and 13. As shown in FIG.14, erosion electrode 100 may define an uninterrupted eroded space 200.Accordingly, flange 22 may be removed, as shown in FIG. 15.

According to some exemplary implementations, erosion electrode 100 mayrotate at least about an axis other than its own central axis. Forexample, as shown in FIGS. 16, 17, and 18, erosion electrode 100 mayhave a central axis parallel to, but not coaxial with, the central axisof fastener 10. Erosion electrode 100 may also be rotated about its owncentral axis. Such rotation(s) may be performed contemporaneously withlongitudinal advancement of erosion electrode 100. According to someexemplary implementations, eroded space 200 resulting from suchoperations may be similar to that shown in FIG. 6 where erosionelectrode 100 is sufficiently narrow, or similar to that shown in FIG.14, where erosion electrode 100 is sufficiently wide. Accordingly,removal of flange 22 may be facilitated thereby.

While the method and agent have been described in terms of what arepresently considered to be the most practical and preferredimplementations, it is to be understood that the disclosure need not belimited to the disclosed implementations. It is intended to covervarious modifications and similar arrangements included within thespirit and scope of the claims, the scope of which should be accordedthe broadest interpretation so as to encompass all such modificationsand similar structures. The present disclosure includes any and allimplementations of the following claims.

It should also be understood that a variety of changes may be madewithout departing from the essence of the disclosure. Such changes arealso implicitly included in the description. They still fall within thescope of this disclosure. It should be understood that this disclosureis intended to yield a patent covering numerous aspects of thedisclosure both independently and as an overall system and in bothmethod and apparatus modes.

Further, each of the various elements of the disclosure and claims mayalso be achieved in a variety of manners. This disclosure should beunderstood to encompass each such variation, be it a variation of animplementation of any apparatus implementation, a method or processimplementation, or even merely a variation of any element of these.

Particularly, it should be understood that as the disclosure relates toelements of the disclosure, the words for each element may be expressedby equivalent apparatus terms or method terms—even if only the functionor result is the same.

Such equivalent, broader, or even more generic terms should beconsidered to be encompassed in the description of each element oraction. Such terms can be substituted where desired to make explicit theimplicitly broad coverage to which this disclosure is entitled.

It should be understood that all actions may be expressed as a means fortaking that action or as an element which causes that action.

Similarly, each physical element disclosed should be understood toencompass a disclosure of the action which that physical elementfacilitates.

Any patents, publications, or other references mentioned in thisapplication for patent are hereby incorporated by reference. Inaddition, as to each term used it should be understood that unless itsutilization in this application is inconsistent with suchinterpretation, common dictionary definitions should be understood asincorporated for each term and all definitions, alternative terms, andsynonyms such as contained in at least one of a standard technicaldictionary recognized by artisans and the Random House Webster'sUnabridged Dictionary, latest edition are hereby incorporated byreference.

Finally, all referenced listed in the Information Disclosure Statementor other information statement filed with the application are herebyappended and hereby incorporated by reference; however, as to each ofthe above, to the extent that such information or statementsincorporated by reference might be considered inconsistent with thepatenting of this/these disclosure(s), such statements are expressly notto be considered as made by the applicant(s).

In this regard it should be understood that for practical reasons and soas to avoid adding potentially hundreds of claims, the applicant haspresented claims with initial dependencies only.

Support should be understood to exist to the degree required under newmatter laws—including but not limited to United States Patent Law 35 USC132 or other such laws—to permit the addition of any of the variousdependencies or other elements presented under one independent claim orconcept as dependencies or elements under any other independent claim orconcept.

To the extent that insubstantial substitutes are made, to the extentthat the applicant did not in fact draft any claim so as to literallyencompass any particular implementation, and to the extent otherwiseapplicable, the applicant should not be understood to have in any wayintended to or actually relinquished such coverage as the applicantsimply may not have been able to anticipate all eventualities; oneskilled in the art, should not be reasonably expected to have drafted aclaim that would have literally encompassed such alternativeimplementations.

Further, the use of the transitional phrase “comprising” is used tomaintain the “open-end” claims herein, according to traditional claiminterpretation. Thus, unless the context requires otherwise, it shouldbe understood that the term “compromise” or variations such as“comprises” or “comprising”, are intended to imply the inclusion of astated element or step or group of elements or steps but not theexclusion of any other element or step or group of elements or steps.

Such terms should be interpreted in their most expansive forms so as toafford the applicant the broadest coverage legally permissible.

1. A method of separating fastener shanks from heads, the method,comprising: Advancing, via electrical discharge machining, a tubularerosion electrode longitudinally through a head and shank of a fastenerwhich is held to a frame via a collar attached to the fastener below theframe; the fastener having a the shank fixed within a hole in the frame;and, forming an eroded space in the shank, below the frame, equal to orless than the diameter of the hole.
 2. The method of claim 1, whereinthe erosion electrode rotates as it is advanced longitudinally.
 3. Themethod of claim 1, the method further comprising applying a voltagedifference between the erosion electrode and at least one of thefastener and the frame.
 4. The method of claim 1, further comprisingattaching a ground electrode configured to contact at least one of thefastener and the frame.
 5. The method of claim 1, further comprising:forming a ligament in the shank between the head and a portion of theshank within the frame.
 6. The method of claim 5, wherein ligament is athickness configured to sever under an external force applied to thefastener, said force being within an acceptable tolerance of the frame.7. The method of claim 5, wherein the ligament is a thickness configuredto sever under the intrinsic stress from the collar applied to thefastener.
 8. The method of claim 1, the method further comprisingproviding a dielectric fluid between the tubular erosion electrode andat least one of the head and shank of the fastener.
 9. A method ofseparating a fastener from two or more frames, comprising: providing ahollow erosion electrode to a to a fastener fixed through and holdingtwo or more frames together; placing the electrode aligned with theshank of the fastener within the frame; fastener having a head coaxiallywith the shank and extending beyond at least a portion of the frames;and, the electrode, via electrical discharge matching, eroding a spacewithin the fastener within the frames, the eroded space having an outerradius less than the outer radius of the shank, whereby a substantiallyconcentric ligament of the shank is formed within the frame, thethickness of the ligament being defined by an offset between the outerradius of the eroded space and the outer radius of the shank.
 10. Themethod of claim 9, creating an eroded space comprises: providing avoltage difference between the erosion electrode and the fastener. 11.The method of claim 9, wherein creating an eroded space comprises:advancing the erosion electrode longitudinally along the axis of thefastener.
 12. The method of claim 9, wherein creating an eroded spacecomprises: rotating the erosion electrode as it is advancedlongitudinally.
 13. The method of claim 9, further comprising: forming athin ligament whereby applying an external force to the head will severthe fastener.
 14. The method of claim 3, wherein the external forcerequired to sever the ligament is within an acceptable tolerance of theframe.
 15. The method of claim 9, wherein the alignment is concentric.16. The method of claim 9, the method further comprising providing adielectric fluid between the tubular erosion electrode and at least oneof the head and shank of the fastener.